The purpose of this study is to investigate an intervention specifically for non-suicidal self-injury (NSSI) in young adults. The goal of this 9-session outpatient intervention is to reduce the frequency and severity of NSSI. During Phase I, 12 patients will be treated in an open pilot trial. During Phase II, 60 patients will be treated in a randomized controlled pilot study in order to determine the feasibility and acceptability of the intervention and to investigate change in NSSI frequency and severity over time.